I'm a bit late noticing this story, about a court case that hinges on determining the "natural" state of the Salt River in Arizona. Specifically, there is interest in determining whether the river was navigable, and at what point in time. Should we consider the state of the river before the Hohokam Classic period, when the Salt River fed thousands of square km of irrigated lands? Was the river in its "natural" state at the time of early European colonization? What about when mammoths roamed the West?
The old nature/culture dichotomy that is so ingrained in Western thought has pretty much broken down in environmentally-focused fields of anthropology. Certainly, the Historical Ecologists have made it abundantly clear that there is no "natural" environment - the landscape was shaped by, with, and through humans, and humans were shaped by, with, and through the landscape.
The legal and environmental policy implications of this realization continue to be problematic. If legal claims to a particular river hinge on understanding its "natural" state, then what period of time should be used to determine the "nature" of the river? If large tracks of the Amazon rainforest were shaped by human hands, then how do we protect and restore those environments by fencing the area off? What does restoration even mean, when there is no "baseline" from which to measure our progress?
These questions aren't unanswerable, or even that difficult to answer, but they require a very different way of thinking about the environment, one that acknowledges the long history of human/landscape interactions and recognizes people as just one more piece of the environmental puzzle.